Fix collect on stateful generator

base/array.jl

@@ -766,13 +766,25 @@ function collect(itr::Generator)
     et = @default_eltype(itr)
     if isa(isz, SizeUnknown)
         return grow_to!(Vector{et}(), itr)
-    else
+    elseif isa(isz, HasLength)
+        len = length(itr)
+        y = iterate(itr)
+        if y === nothing
+            return et[]
+        end
+        v1, st = y
+        return collect_to_with_first!(Vector{typeof(v1)}(undef, len), v1, itr, st)
+    elseif isa(isz, HasShape)
+        axs = axes(itr)
         y = iterate(itr)
         if y === nothing
-            return _array_for(et, itr.iter, isz)
+            return similar(Array{et,length(axs)}, axs)
         end
         v1, st = y
-        collect_to_with_first!(_array_for(typeof(v1), itr.iter, isz), v1, itr, st)
+        arr = similar(Array{typeof(v1),length(axs)}, axs)
+        return collect_to_with_first!(arr, v1, itr, st)
+    else
+        error("unreachable")
     end
 end
 

test/iterators.jl

@@ -292,6 +292,15 @@ let (a, b) = (1:3, [4 6;
     end
 end
 
+# collect stateful iterator
+let
+    itr = (i+1 for i in Base.Stateful([1,2,3]))
+    @test collect(itr) == [2, 3, 4]
+    A = zeros(Int, 0, 0)
+    itr = (i-1 for i in Base.Stateful(A))
+    @test collect(itr) == Int[] # Stateful do not preserve shape
+end
+
 # with 1D inputs
 let a = 1:2,
     b = 1.0:10.0,
@@ -860,4 +869,4 @@ end
     @test Iterators.peel(1:10)[2] |> collect == 2:10
     @test Iterators.peel(x^2 for x in 2:4)[1] == 4
     @test Iterators.peel(x^2 for x in 2:4)[2] |> collect == [9, 16]
-end
+end